This proposal seeks to acquire a point-scanning confocal fluorescence microscope for the Center for Cell Imaging at Yale University School of Medicine. The ongoing renaissance in the use of light microscopy for cell and molecular biology and physiology has been driven in large part by the development of specific fluorescent probes of cell structure and function, coupled with confocal fluorescence microscope systems that extend our abilities to visualize and quantitate such probes in cells and tissues. Laser scanning confocal microscopy, because of its ability to "optically section" cells and tissues, provides a tool with the spatial resolution needed to define structure in live and fixed cells alike, along with the temporal resolution to follow dynamic processes in living cells. Specific projects that would take immediate advantage of this equipment include regulation of osteoclast function and bone resorption, MHC transport in dendritic cells, establishment of polarity in epithelia and neurons, molecular basis for bile secretion and cholestasis, regulation of oogenesis, and subcellular mechanisms of calcium signaling. Although our facility already has a confocal microscope and a two photon microscope, these are so heavily used that an additional confocal microscope now is needed to assure that our investigators will continue to have adequate access to state-of-the-art imaging techniques.